The present invention relates in general to couplings for joining tubular conduits, and in particular to a grip coupling having an interior grip ring for securing tubular conduit to the grip coupling.
Prior art connectors and fittings have been utilized for joining to tubular conduits for connecting the tubular conduits to other members. The tubular conduits have included electrical conduits, piping, ducting and the like, which have been used for both fluid flow conduits and to provide protective enclosures for electrical power and telecommunication cables. For power and telecommunication cable installations which are buried or located in hazardous environments, a fluid tight seal is provided between the fitting and the mating ends of the tubular conduits. Recently, tubular conduits made of polyethylene have been provided for running telecommunication cables, such as fiber optic cables. In the prior art, fittings typically have been joined to the terminal ends of sections of such tubular conduits by either adhesive bonding, swedging or securing two mating threads together. Securing a fitting to a conduit end requires preparation to clean the surfaces of the conduit end for bonding to an adhesive, which is labor intensive. Swedged fittings require that swedging members be placed on opposite sides of a terminal end section of a tubular conduit so that the end of the conduit may be squeezed between the two swedging members. One of the swedging members is placed on the interior of the tubular conduit which results in a restriction which is smaller than the interior diameter of the tubular conduit, rather than providing a full boar opening. It is also preferable in some circumstances that conduit couplings be of a slim-line, or smaller, outside diameter. Swedging may also cause problems with tubular conduits made of polyethylene since polyethylene is subject to creep under pressure, causing the polyethylene material to cold flow and weaken the grip of the swedging members upon the tubular conduit. A threaded connection requires the threading of either an interior surface or an exterior surface of the tubular conduit, which is both time consuming and labor intensive.
The prior art also includes grip couplings, that is, couplings which are self-gripping when secured to the ends of tubular conduits. One example is that shown is U.S. Pat. No. 6,059,321, entitled xe2x80x9cGRIP COUPLING FOR JOINING CONDUIT,xe2x80x9d invented by Lucian H. Lyall, III, and issued on May 9, 2000 to Group Timberline, Inc. of Kingwood, Tex., Assignee of the present application. U.S. Pat. No. 6,059,321 discloses a grip coupling having interiorly threaded ends which define interiorly disposed thread crests that extend with edges for scoring the exterior periphery of the tubular conduit being joined, such that when the coupling is rotated, the threads will grippingly engage the tubular conduit and pull the tubular conduit further within the grip coupling to secure the tubular conduit within the grip coupling. Other self-gripping couplings for joining tubular conduit having included tabs, or barbs, which are formed in the interior of the couplings for cutting into the exterior periphery of conduit being joined therewith to secure the tubular conduit within the grip couplings. In the prior art, grip couplings are typically required to hold against minimum specified pull out forces in excess of five hundred pounds. Prior art tubular conduit couplings typically require greater force for securing such a coupling to a tubular conduit than the average person could reasonably exert without the aid of tooling for securing tubular conduit to couplings which can achieve pull out ratings in excess of five hundred pounds.
A grip coupling is provided for securing tubular conduit. The grip coupling has two coupling body halves which are joined along weld lines at a central portion of the grip coupling. Each of the coupling body halves has a tapered entrance section and an interior seal which is provided adjacent the tapered entrance section of the grip coupling, inboard of the tapered entrance section and preferably integrally formed with the body of the grip coupling. Two annular-shaped shoulders are formed in the interior surfaces of each of the coupling body halves, with the annular-shaped shoulders facing inboard relative to respective coupling body halves and being spaced apart when the two coupling body halves are joined together. Two grip rings are disposed within respective ones of the two coupling body halves, fitting against respective ones of the two annular-shaped shoulders. The grip rings each preferably have a continuous, annular shaped grip ring body, grip teeth which extend from the grip ring body, and a tapered exterior periphery which tapers inward in extending from the grip ring body to the grip teeth. The grip rings are installed in respective ones of the two coupling body halves, with a spacer ring disposed therebetween and the grip teeth disposed inboard of the grip ring body, and then the two coupling body halves are joined together. The spacer ring preferably has two interiorly disposed, tapered surfaces which taper radially inward within the spacer ring in an outboard direction relative to the grip coupling and which may seal the terminal end of a tubular conduit.